Always check the player status screen before selling a player. If a player has a close friend on the team, this will cost tons of morale. This could be disastrous if the remaining player is one of your stars.
For easy cash, go into Club/Stadium Facilities/Stadium Expansion. Change the stadium type (rounded corners, oval; this will cost you money) and select "Build Stadium". Repeat this (changing the stadium type, build it), and you will receive money. Note: Do not do this if you are thinking about building a new stadium.
At the start of the game or after any season is over, go into the transfer market and search with the following details:
All Players Transfer Limit : £0 Min Potential : (whatever standard of player you need) Position : (whatever you need) Side : (whatever you need) Age : Any Search : All Counties
Once done, the game will display all the players above your potential level who have been released. It is possible to sign Henry, Terry, and Ronaldinho this way. Note: You may need to wait until a particular player becomes available.